JPH0513828B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an organic composite steel plate having excellent corrosion resistance, weldability, and workability. That is, the present invention provides an organic composite steel sheet in which various galvanized steel sheets are subjected to special chromate treatment, and then a special organic resin containing colloidal silica with a specific fine grain size is coated in a specific proportion. It is. [Prior Art] As is well known, electrogalvanized steel sheets, hot-dip galvanized steel sheets, and various alloy-plated steel sheets are widely used in automobiles, home appliances, building materials, and the like. Under these circumstances, in recent years, there has been an increasingly strong demand for surface-treated materials with particularly excellent corrosion resistance, and the demand for such steel sheets is likely to increase further in the future. For example, in the home appliance industry, there is a demand for a steel plate with excellent corrosion resistance that can be used bare and omit painting from the viewpoint of process and cost savings. In addition, recent environmental changes in the automobile industry include corrosion caused by rock salt, which is sprayed to prevent roads from freezing in winter in North America and Northern Europe, and corrosion caused by acid rain caused by the generation of SO ₂ gas in industrial areas. Vehicle bodies are exposed to severe corrosive environments, and from a safety standpoint, there is a strong demand for surface-treated steel sheets with excellent corrosion resistance. In order to solve these problems, various studies have been made and many products have been developed. Until now, galvanizing has been carried out to improve the corrosion resistance of steel sheets. Galvanized steel sheets prevent corrosion of the steel sheet through the sacrificial anticorrosive action of zinc, and in order to obtain corrosion resistance, the amount of zinc deposited must be increased. For this reason, there are several problems such as an increase in the cost of the required amount of zinc and a decrease in workability, weldability, and productivity. Additionally, galvanized steel sheets generally have poor paint adhesion. As a method for improving the corrosion resistance of such galvanized steel sheets, various alloy-plated steel sheets have been developed. For example, these alloy-plated steel sheets include
Zn-Ni series, Zn-Ni-Co series, Zn-Ni-Cr series, Zn
-Fe system, Zn-Co system, Zn-Mn system, etc. can be mentioned. It is recognized that these alloy platings improve the corrosion resistance of bare steel sheets by about 3 to 5 times compared to ordinary galvanized steel sheets. However, the problem is that white rust or red rust is likely to occur if left outdoors for a long period of time or if water or salt water is sprayed on it. There is also a method of applying chromate treatment after plating to improve corrosion resistance, which is quite effective, but in high temperature, high humidity or salt-containing atmospheres,
White rust occurs after 150 hours. In order to further improve corrosion resistance, various resins are applied to the chromate-treated zinc-plated steel sheets.
So-called simple pre-coated steel sheets (hereinafter referred to as organic composite steel sheets) have been developed and some are commercially available. An example is listed below. JP-A-58-210190, JP-A-58-210192 Chromate treatment is applied to a zinc-based alloy single-layer plating or double-layer plating, and conductive substances (Zn, Al,
A weldable coated steel plate coated with a resin paint containing (Sn, Fe, Ni, Co, Cr, Mn) for the purpose of improving weldability, paint film adhesion, and corrosion resistance. JP-A-58-224174 A method for producing highly corrosion-resistant rust-preventive coated steel sheets in which the surface of a zinc alloy-plated steel sheet is subjected to paint-on chromate treatment, and then treated with a composite organic silicate resin solution without washing with water. For the purpose of improvement. JP-A-59-116397 The steel plate has a highly corrosion-resistant electroplated layer such as Ni-Zn or Fe-Zn as the first layer on both sides, and a thin electroplated layer such as Fe-Zn on one side as the second layer. The coating layer is made of a highly corrosion-resistant and rust-preventing steel plate that has a resin containing conductive pigments or a resin film with a thickness of 0.5 to 3.0μ on the other side, and the outer side has corrosion resistance and paint adhesion, and the inner side has spot weldability. , for the purpose of imparting processability. Japanese Patent Publication No. 61-36587 This is a surface treatment method for electrogalvanized steel sheets in which a chromate film is formed on the surface of the electrogalvanized steel sheet, and then a special resin aqueous solution containing colloidal silica is applied and dried to improve fingerprint resistance. , paint adhesion, hardness,
Aimed at improving corrosion resistance. JP-A-60-149786 A processing method that is different from the above-mentioned JP-B No. 61-36587, the base plating is limited to a zinc-based alloy, and a resin different from that of JP-A-61-36587 is used. This is a surface treatment method that adds even more corrosion resistance and solvent resistance to the above. JP-A No. 61-167545 A high-quality zinc-based alloy plated layer in which a chromate treatment is applied to a zinc-based alloy plating layer, and a paint containing one or both of hard metal powder, hard carbonized powder, and zinc powder is applied thereon. Corrosion-resistant weldable painted steel plate designed to improve corrosion resistance and weldability. All of the above-mentioned steel sheets are called organic composite steel sheets, and have improved various properties. [Problems to be solved by the invention] However, even in these cases, the corrosion resistance cannot necessarily be said to be sufficient in a harsh corrosive environment, and
If the thickness of the outermost resin layer is increased to ensure corrosion resistance, welding becomes difficult. Furthermore, organic coatings are generally prone to scratches during continuous pressing or bead processing, so build-up is likely to occur, and it is difficult to stably ensure corrosion resistance. Therefore, it cannot be practically used as a rust-preventing steel plate for automobile bodies. As described above, conventional organic composite steel sheets have been insufficient to simultaneously have excellent corrosion resistance, weldability, and workability (continuous pressability and bead workability). In contrast, the present invention provides an organic composite steel sheet that has ultra-high corrosion resistance, is excellent in welding, and has extremely excellent workability. [Means for Solving the Problems] The present invention has a plating layer as a first layer on the surface of a steel sheet, and an electrolytic chromate layer as a second layer, and this chromate layer has Cr ₂ O in the chromate layer. The ratio of ₃ is 60% or more and the total chromium amount is 40 to 120 mg/m ²
belongs to. And as the third layer, the particle size is 1~
This is an organic composite steel sheet having a 0.5-3μ thick water-based resin layer made of an olefin/acrylic acid copolymer with an olefin copolymerization ratio of 70-95% and containing 15-40 (wt)% colloidal silica of 10mμ. The basic structure of the organic composite steel sheet of the present invention has the above-mentioned first to third layers on both sides of the steel sheet, as shown in FIG. 18a. Here, the plating layer refers to Zn, Sn, Cu, Cr, Ni,
Co may be plated alone or with two or more alloys selected from these, and plating may be carried out alone or in multiple layers, but Zn--Ni alloy plating is most preferred. Details will be explained below. [Electrolytic Chromate Layer] As a result of detailed study, the present inventors found that the chromate layer formed on the surface of a plated steel sheet must satisfy the following conditions. In other words, it must be an electrolytic chromate layer mainly composed of Cr ₂ O ₃ . Generally, with coated or reactive chromate, the film is formed mainly through a substitution reaction with ions eluted from the plating layer, so it is difficult to form a strong film that can withstand harsh processing.For example, chromate film When an organic film is formed on the material and pressed, the chromate film is maintained during light processing, but when the processing is severe, the chromate film itself is destroyed and the organic film peels off. On the other hand, with electrolytic chromate, the film is formed mainly by the precipitation of ions from the chromate bath, so a strong and dense film is likely to be formed. Therefore, electrolytic chromate is more advantageous as a chromate film that can be processed. However, as a result of detailed study by the present inventors, we found that chromate for the base of organic composite steel sheets cannot be used unless the ratio of Cr ₂ O ₃ in the film formed in electrolytic chromate satisfies the following conditions. I found out that this is not the case. Cr ₂ O ₃ amount in chromate film / total chromate film amount x 100
=60% or more In other words, the electrolytic chromate layer in the present invention is
It is mainly composed of Cr ₂ O ₃ and suppresses the formation of residual metallic chromium and chromium hydroxide that form the chromate layer. By forming an electrolytic chromate film that satisfies the above conditions on a plated steel sheet and then forming a special organic film thereon, an organic composite steel sheet with excellent properties can be obtained. The method for analyzing Cr ₂ O ₃ in the electrolytic chromate layer is to apply X-rays or electron beams while sequentially removing the chromate layer, measure and integrate the binding energy of each component, and separate the waveforms. The amount of Cr ₂ O ₃ was calculated using the following method. Figure 1 shows the total amount of chromium deposited on a Zn-Ni alloy coated steel sheet with various proportions of Cr ₂ O ₃ in the chromate film, 70 mg/
An electrolytic chromate layer of m ² (constant) is applied, and on top of that, colloidal silica with a particle size of 5 to 7 mμ is added to an aqueous resin dispersion of olefin/acrylic acid copolymer resin with an olefin copolymerization ratio of 80%. 20%
After drying the aqueous liquid adjusted to (wt%)
_Cr2 in the chromate layer
This figure shows the relationship between the amount of O ₃ and the removability of the organic film after press working. Here, the test conditions were a blank diameter of 90 mmφ, a die surface roughness of #120, and press processing was performed under the conditions shown in Figure 2.
The peelability of the film was investigated. In the figure, 1 indicates a steel plate, A indicates a punch, and B indicates a die. The state of peeling of the film was evaluated by peeling off the tape from the processed area after processing and determining the blackening rate of the tape (the more the film peels off, the higher the blackening rate). As is clear from Figure 1, the adhesion of the organic film during processing varies greatly depending on the proportion of Cr ₂ O ₃ in the electrolytic chromate layer, and excellent adhesion is ensured when the Cr ₂ O ₃ content is 60% or more. Ru. Furthermore, FIG. 3 shows the corrosion resistance of a flat plate treated in the same manner. The corrosion resistance was determined by a salt spray test in accordance with the JIS-Z-2371 standard (salt water concentration 5%, tank temperature
The rusting condition after 4000 hours (35°C, spray pressure 20psi) was investigated and evaluated in five grades: ◎, ○, △, ×, and XX, with ◎ being the best. ◎: Red rust occurrence 0% ○:〃 0~1% △:〃 1~10% ×:〃 10~50% XX:〃 50% or more As is clear from Figure 3, Cr ₂ O in the electrolytic chromate layer The corrosion resistance of the organic composite steel plate in the processed part varies greatly depending on the ratio of ₃ , and excellent corrosion resistance is ensured when Cr ₂ O ₃ is 60% or more. Figure 4 shows a Zn-Ni alloy coated steel sheet with the proportion of Cr ₂ O ₃ in the electrolytic chromate layer kept constant at 90%, the total amount of chromium deposited is changed, and the same as in Figure 1 is applied. This figure shows the relationship between the total amount of chromium deposited and the peelability of the film after press working when 1.5μ of organic resin is applied. As is clear from Figure 4, the total amount of chromium deposited is 40 mg/m ² ~
The peelability of the film is good at 120 mg/m ² . Further, the flat plate corrosion resistance of the same treated material is shown in FIG. 5 (the test method is the same as in FIG. 3). The total amount of chromium deposited was 40 mg/m ² to 120 mg/m ² , showing good corrosion resistance of the flat plate. From the above results, the optimum total amount of chromium deposited in the electrolytic chromate layer is 40 to 120 mg/ ^m2 . The method of obtaining an electrolytic chromate layer containing 60% or more of Cr ₂ O ₃ in the present invention is, for example, by electrolytic treatment using a Cr ₂ O ₃ -heavy metal ion-halogen bath. Specific methods, such as concentration ranges, are proposed as a method for surface treatment of metals, for example, in Japanese Patent Publication No. 14457/1983. The adoption of the electrolytic chromate treatment method as the chromate treatment in the production of organic composite steel sheets is disclosed in the above-mentioned Japanese Patent Laid-Open No. 58-210190 and Japanese Patent Laid-Open No. 58-1989.
It is described in Publication No. 210912. However, in the conventional electrolytic chromate treatment, as in the present invention, the ratio of Cr ₂ O ₃ in the chromate film and the adhesion of the organic film,
Nothing is disclosed regarding the relationship with corrosion resistance. [Plating layer] On the other hand, as a result of forming the electrolytic chromate layer of the present invention for various platings, the present inventors found that when Ni is included in the plating, the electrolytic chromate layer is chemically degraded by the presence of Ni. It was found that a stable and dense film was formed. Figure 6 shows the elution of chromium when EG (electrogalvanized steel sheet), Zn-Fe alloy-plated steel sheet, and Zn-Ni alloy-plated steel sheet are subjected to the known CrO ₃ −SO ₄ ^--- based chromate treatment. It shows the gender. The Cr ₂ O ₃ content in the formed chromate layer was around 40%. In addition, Figure 7 shows the results of electrolytic chromate treatment of EG, Zn-Fe alloy-plated steel sheets, Zn-Ni alloy-plated steel sheets, and Ni thin-plated steel sheets using the aforementioned CrO ₃ -heavy metal ion-halogen system. This shows the elution of chromium in the layer. The Cr ₂ O ₃ content of the formed chromate layer was around 80%. As shown in Figures 6 and 7, a stable chromate layer that is difficult to dissolve is formed due to the presence of Ni in the plating, but it is especially clear from Figure 7 that Cr ₂
A chromate layer with a high O ₃ ratio is more stable and less soluble than a chromate layer with a low Cr ₂ O ₃ ratio (Figure 6) due to the presence of Ni in the base material. be. Figure 8 shows EG, Zn-Fe alloy coated steel sheets and Zn
- Chromate treatment of Ni-based alloy plated steel sheet with conventional CrO ₃ SO ₄ ^-based bath (Cr ₂ O ₃ 40%) and CrO ₃ -heavy metal ion-halogen based bath (Cr ₂ O ₃ 80%) according to the present invention This shows the corrosion resistance when The evaluation method is the same as in Figure 3, but the salt spray time is
The rusting status after 600 hours was investigated and similarly evaluated on a five-point scale. As is clear from Figure 8, the electrolytic chromate layer with a high Cr ₂ O ₃ ratio (approximately 80%) forms a dense film with high coverage due to the presence of Ni in the material, and has extremely excellent corrosion resistance. It shows. These effects of Ni only need to be present in the plating layer in any plating system, and the same effects can be obtained even if Ni is flash plated on a plating layer that does not contain Ni or on a cold-rolled steel sheet. Effects can be obtained. [Colloidal silica-containing olefin/acrylic acid copolymerized water-based resin layer] Next, Figure 9 shows an electrolytic chromate layer (with a Cr ₂ O ₃ ratio of 90% and a total Cr
Colloidal silica with ^a particle size of 5 to 7 mμ is applied to an aqueous resin dispersion of olefin/acrylic acid copolymer resin with various copolymerization ratios of olefin and acrylic acid. The relationship between the copolymerization ratio of olefin and acrylic acid and paint adhesion is shown when three coats of paint are applied to a test piece coated with an aqueous solution containing 20% of acrylic acid to a thickness of 1.5μ after drying. . For the paint adhesion test, cationic ED was applied to the above test piece.
The coating was 20 μm, and the intermediate coat and top coat were each 30 μm each. After that, it was immersed in distilled water at 50°C for 10 days, and then the paint film was cut into 2 mm squares and peeled off with tape, and the peeled area was evaluated. ◎: Peeling area 0% ○: 0-1% △: Peeling area 1-10% ×: 10-50% XX: 50% or more As is clear from Figure 9, olefin/acrylic acid copolymer When the copolymerization ratio of olefin in the resin is 70% or more, extremely excellent paint adhesion is exhibited. Furthermore, FIG. 10 shows the results of the corrosion resistance of a bare flat plate without coating when the copolymerization ratio of olefin/acrylic acid was changed. Corrosion resistance is the same as in Figure 3.
It was conducted in accordance with the JIS-Z-2371 standard. As is clear from FIG. 10, when the copolymerization ratio of olefin in the olefin/acrylic acid copolymer resin is 70% or more, it exhibits extremely excellent corrosion resistance, and when it is 95% or more, the corrosion resistance slightly decreases. From the above results, the range in which the olefin/acrylic acid copolymer resin satisfies paint adhesion and corrosion resistance at the same time is an olefin copolymerization ratio of 70 to 95%. Next, the addition of colloidal silica to the aqueous resin dispersion of olefin/acrylic acid copolymer resin will be described. It is already a well-known fact that colloidal silica is included in an organic resin film, and is also disclosed in the aforementioned Japanese Patent Publication No. 61-36587 and Japanese Patent Application Laid-Open No. 60-149786, which increases the hardness of an organic resin film. Colloidal silica is added to. However, as a result of detailed studies, the present inventors found that adding a specific amount of fine colloidal silica to an aqueous resin dispersion of olefin/acrylic acid copolymer resin improves the lubricity of the film, rather than adding it to other types of resin. It has been found that the lubricity of the film is significantly improved, and that the lubricity of the film is further improved when the olefin copolymerization ratio of the olefin/acrylic acid copolymer resin falls within a specific range. Figure 11 shows an electrolytic chromate layer (Cr ₂ O ₃ ratio of 90%, total Cr coating amount of 70 mg/m ² ) formed on a Zn-Ni alloy plated steel sheet, and a co-coated layer of olefin and acrylic acid deposited on top of it. Colloidal silica with different particle sizes was added to an aqueous resin dispersion of olefin/acrylic acid copolymer resin with a different polymerization ratio to give a concentration of 20%, and after drying, it was coated to a particle size of 1.5μ. This figure shows the relationship between the polymerization ratio, the particle size of colloidal silica, and sliding resistance. As is clear from FIG. 11, the sliding resistance is significantly affected by the particle size of colloidal silica, and when the particle size of colloidal silica is 1 to 10 mμ, the sliding resistance is significantly reduced. That is, the lubricity of the film is greatly improved. On the other hand, the effectiveness of ultrafine colloidal silica also depends on the copolymerization ratio of olefin;
The strongest effect appears in the 70-95% range. Moreover, FIG. 12 shows the corrosion resistance of the processed portion of the same test piece in FIG. 11 after press working. The evaluation is the same as in Figure 3. As is clear from FIG. 12, the corrosion resistance of the processed part is significantly affected by the particle size of colloidal silica, and the corrosion resistance is greatly improved when the particle size of colloidal silica is in the range of 1 to 10 mμ. Further, the effect of ultrafine colloidal silica is influenced by the copolymerization ratio of olefin, and the effect is most pronounced when the copolymerization ratio is in the range of 70 to 95%. Furthermore, Figure 13 shows how the weldability (continuous spot weldability) changes using the same test piece as in Figure 11 (however, the olefin/acrylic acid copolymerization ratio is constant at 80%). . The continuous welding test was evaluated by continuous welding points until the nugget diameter reached 4 mmφ. ◎: 5000 points or more ○: 4500-5000 points △: 4000-4500 points ×: 3500-4000 points ××: 3500 points or less As is clear from Figure 13, weldability is significantly affected by the particle size of colloidal silica. Weldability is greatly improved when the grain size of the receiving colloidal silica is in the range of 1 to 12 mμ. From the above results, the best sliding resistance, corrosion resistance of processed parts, and weldability can be achieved at the same time when the olefin/acrylic acid copolymer resin has an olefin copolymerization ratio of 70 to 95% and a particle size of colloidal silica. The optimum value is 1 to 10 mμ. Next, Figure 14 shows that an electrolytic chromate layer (Cr ₂ O ₃ ratio of 90% and total chromium deposition amount of 70 mg/m ² ) is formed on a Zn-Ni alloy-plated steel sheet, and olefin copolymerization is applied on top of it. Colloidal silica of 5 to 7 mμ was mixed in various ratios to olefin/acrylic acid copolymer resin with a ratio of 80%, and applied to 1.5μ, and the relationship between the mixing ratio of colloidal silica and sliding resistance was determined. It is. As is clear from FIG. 14, the sliding resistance is affected by the amount of colloidal silica added, and when the amount of colloidal silica is 15% or more, the sliding resistance is significantly reduced. However, if it exceeds 40%, although the sliding resistance effect is maintained, colloidal silica builds up during continuous pressing, which is not desirable. FIG. 15 shows the corrosion resistance of the processed portion of the same test piece as in FIG. 14 after press working. The evaluation is the same as in Figure 3. As is clear from FIG. 15, the corrosion resistance of the processed part is significantly affected by the amount of colloidal silica added, and excellent corrosion resistance is exhibited when the amount of colloidal silica added is 15 to 40%. From the above results, the amount of colloidal silica added to the olefin/acrylic acid copolymer resin is 15 to 40.
%. As mentioned above, the inclusion of colloidal silica in an organic film for the purpose of improving the hardness of the organic film is disclosed in the above-mentioned Japanese Patent Publication No. 36587/1983 and Japanese Patent Application Laid-open No. 60/1983.
It is known from Japanese Patent Laid-open No. 149786, and on the other hand, it is also known to incorporate metal powder etc. into an organic film in order to improve the weldability of the organic film. It is known from the official gazette. In contrast, in the present invention, by selecting colloidal silica with a particle size of 1 to 10 mμ and incorporating it into a specific organic film, we have simultaneously achieved lubricity, corrosion resistance of processed parts, and weldability. This is significantly different from the conventional technology. On the other hand, FIG. 16 shows organic composite steel sheets with a conventional organic film (urethane) and a 5-
This figure shows the continuous spot weldability of an olefin/acrylic acid copolymer resin containing 20% ultrafine colloidal silica particles with a diameter of 7 mμ when the thickness of the organic film is varied. As is clear from Figure 16, weldability of ordinary organic films decreases when the film thickness exceeds 0.5 μm, whereas the film according to the present invention can be easily welded to a thickness of 3.0 μm, and has significantly improved weldability. I can see that it has improved. Next, FIG. 17 shows the relationship between the film thickness and corrosion resistance of the organic film in the present invention. As is clear from FIG. 17, excellent corrosion resistance is exhibited when the film thickness is 0.5μ or more. Based on the above weldability and corrosion resistance test results, in the present invention, the thickness of the organic film is set to 0.5 to 3.0 μm. The basic structure of the organic composite steel sheet of the present invention is shown in Figure 18a.
As shown in , the steel plate 1 has three layers on both sides: a first layer (plating 2), a second layer (electrolytic chromate layer 3), and a third layer (organic film 4 containing colloidal silica). The steel sheet as a whole has high corrosion resistance, and when this steel sheet is used as a rust-preventing steel sheet for an automobile body, an organic film is present under the outer coating, so that low-temperature chipping resistance is improved. However, in the present invention, the first
Also includes those shown in Figures 8 b and c. That is, Fig. 18b
has the first to third layers on one side only, and the other side is the steel plate surface 5, Figure 18c has the first to third layers on only one side, Other side plating layer 2
It has a plating surface 6. Further, in some cases, as shown in b and c, an electrolytic chromate layer 7 having the same composition as the second electrolytic chromate layer 3 may be formed on the steel plate surface 5 or the plating surface 6. In this case, the total amount of chromium in the electrolytic chromate layer 7 is desirably 3 mg/m ² or less in view of the chemical conversion properties shown in FIG. 19. [Example] Examples will be described below. Example 1 Cr ₂ in the chromate film was applied to a Zn-Ni alloy coated steel sheet (NI = 11.0%) with a plating weight of 20 g/m ²
Electrolytic chromate treatment is applied so that the O ₃ content is 90% and the total chromium adhesion amount is 60 mg/m ² (treatment conditions are described later, the same applies hereinafter), and then olefin/acrylic acid with an olefin copolymerization ratio of 80% is applied. An aqueous solution containing colloidal silica with a particle size of 5 to 7 mμ adjusted to 20% (wt%) is applied onto the aqueous resin dispersion of the copolymer resin, and dried to yield 1.5 g/m ^{2 .}
A film was formed so that Example 2 Total chromium adhesion with 95% Cr ₂ O ₃ in the chromate film on ^a Zn-Ni-Co alloy plated steel sheet (Ni = 11.5%, Co = 0.3%) with a plating weight of 20 g/m 2 Electrolytic chromate treatment is applied to the amount of 70 mg/ ^m2 , and on top of that, colloidal particles with a particle size of 1 to 3 mμ are added to an aqueous resin dispersion of olefin/acrylic acid copolymer resin with an olefin copolymerization ratio of 85%. silica
An aqueous solution adjusted to 30% (weight %) was applied thereon and dried to form a film having a concentration of 1.3 g/m ² . Example 3 Electrolytic chromate treatment was applied to a Zn-Fe alloy coated steel sheet with a plating weight of 20 g/m ² so that the Cr ₂ O ₃ in the chromate film was 75% and the total chromium adhesion was 90 mg/m ² Then, colloidal silica with a particle size of 4 to 5 mμ was adjusted to 35% (wt%) in an aqueous resin dispersion of olefin/acrylic acid copolymer resin with an olefin copolymerization ratio of 95%. Apply the aqueous solution on top of it and dry it to give 1.0g/m ²
A film was formed so that Example 4 Total chromium adhesion with 90% Cr ₂ O ₃ in the chromate film on a Zn-Ni-Cr alloy coated steel sheet (Ni = 10.8%, Cr = 0.8%) with a plating weight of 20 g/m ² Electrolytic chromate treatment is applied so that the amount is 70 mg/m ² , and on top of that, colloidal particles with a particle size of 8 to 10 mμ are added to an aqueous resin dispersion of olefin/acrylic acid copolymer resin with an olefin copolymerization ratio of 82%. An aqueous solution containing 17% silica (by weight) was applied thereon and dried to form a film having a concentration of 1.8 g/m ² . Example 5 Cr ₂ in the chromate film was applied to a Zn-Mn alloy plated steel sheet (Mn = 32%) with a plating weight of 20 g/m ²
An aqueous resin dispersion of olefin/acrylic acid copolymer resin, which is electrolytically chromated so that the O ₃ content is 95% and the total chromium adhesion is 105 mg/m ² , and the olefin copolymerization ratio is 78%. An aqueous solution containing 25% (weight %) colloidal silica having a particle size of 4 to 6 mμ was applied thereon and dried to form a film having a concentration of 2.0 g/m ² . Example 6 A Zn-Fe alloy plated steel plate (Mn=32%) with a plating weight of 20 g/m ² was flat-plated with 150 mg/m ² of Ni, and Cr ₂ O ₃ in the chromate film was then plated on top of it.
Electrolytic chromate treatment is applied so that the total amount of chromium deposited is 85mg/ ^m2 at 90%, and then the particle size is added to an aqueous resin dispersion of olefin/acrylic acid copolymer resin with an olefin copolymerization ratio of 85%. 2~
An aqueous solution containing 4 mμ of colloidal silica adjusted to 23% (wt%) was applied thereon and dried to form a film having a concentration of 1.8 g/m ² . Example 7 A cold-rolled steel sheet was plated with 150 mg/m ² of Ni flash, and electrolytic chromate treatment was applied thereto so that the Cr ₂ O ₃ in the chromate film was 98% and the total amount of chromium deposited was 80 mg/m ² . In addition, colloidal silica with a particle size of 1 to 2 mμ was adjusted to 30% (wt%) in an aqueous resin dispersion of olefin/acrylic acid copolymer resin with an olefin copolymerization ratio of 93%. Apply aqueous liquid on it and dry it to 2.0
A film was formed so that the weight was 1.2 g/m ² . Example 8 Double-sided plated plate with a coating weight of 20g/ ^m2
Zn-Ni alloy plated steel plate (Ni = 11.2% on both sides)
Electrolytic chromate treatment was applied to one side of the chromate film so that the Cr ₂ O ₃ in the chromate film was 90% and the total chromium adhesion amount was 80 mg/m ² , and on top of that an olefin/olefin copolymerization ratio of 85% was applied. An aqueous solution containing colloidal silica with a particle size of 4 to 6 mμ adjusted to 20% (wt%) is applied onto an aqueous resin dispersion of acrylic acid copolymer resin, and dried to give a 1.5 mμ
A film was formed so that the weight was 1.2 g/m ² . In addition, a single-sided organic composite steel plate was manufactured in which the other side remained plated. Example 9 Double-sided plated plate with a coating weight of 20g/ ^m2
Zn-Ni alloy plated steel plate (Ni = 11.2% on both sides)
Electrolytic chromate treatment was applied to one side of the chromate film so that the Cr ₂ O ₃ in the chromate film was 90% and the total chromium adhesion amount was 75 mg/m ² , and on top of that an olefin/olefin copolymerization ratio of 81% was applied. An aqueous solution of colloidal silica with a particle size of 3 to 5 mμ adjusted to 23% (wt%) is applied onto an aqueous resin dispersion of acrylic acid copolymer resin, and dried to give a 1.4% (wt%) aqueous solution.
A film was formed so that the weight was 1.2 g/m ² . In addition, a one-sided organic composite steel sheet having a chromate layer with a chromium adhesion amount (remaining amount after removal) of 1.5 mg/m ² on the other side was manufactured. Comparative Example 1 Zn-Ni alloy coated steel plate with a coating weight of 20 g/m ² (Ni=11.0%). Comparative Example 2 A Zn-Ni alloy plated steel sheet (Ni = 11.5%) with a plating weight of 20 g/m ² and a total Cr coating weight of 70
Steel plate coated with chromate treatment to achieve mg/ ^m2 . Comparative Example 3 A Zn-Ni alloy plated steel sheet (Ni = 10.9%) with a plating weight of 20 g/m ² and a total Cr coating weight of 50
^Reactive chromate treatment is applied to give a concentration of 1.3
A film was formed so that the weight was 1.2 g/m ² . Comparative Example 4 A Zn-Ni alloy plated steel sheet (Ni = 11.2%) with a plating weight of 20 g/m ² and a total Cr coating weight of 90
Apply chromate treatment to give 20% (wt%) of colloidal silica with a particle size of 17 to 20 mμ on the acrylic resin ^, and then dry it. A film was formed at a density of 1.2 g/m ² . Comparative Example 5 A double-sided plated plate with a coating weight of 20g/ ^m2 .
Zn-Ni alloy plated steel plate (Ni = 11.3% on both sides)
Coating-type chromate treatment was applied to one side of the urethane resin so that the total amount of chromium deposited was 95 mg/ ^m2 , and colloidal silica with a particle size of 17 to 20 mμ was applied to the urethane resin.
% (weight %) was applied thereon and dried to form a film having a weight of 1.3 g/m ² . In addition, a one-sided organic composite steel sheet having a chromate layer with a chromium adhesion amount (remaining amount after removal) of 4.5 mg/m ² on the other side was manufactured. Electrolytic chromate method: Bath composition: _CrO3 50g/Co ⁺⁺ 1~4g/Cl ^- 0.05~0.4g/(Controlled according to the _amount of _Cr2O3 ) Bath temperature: 55℃ D _K : 5A/dm ² Electricity :3~ depending on the total amount of chromium deposited
Table 1 shows the results of various tests conducted on the surface-treated steel sheets obtained in Examples 1 to 9 and Comparative Examples 1 to 5, controlled at 10 C/dm ² .

【table】

[Table] Various test conditions are as follows. (a) Corrosion resistance of flat plate By salt spray test in accordance with JIS-Z-2321
The white rust occurrence rate (%) after 2000 hours and the red rust occurrence rate (%) after 4000 hours were determined. (b) Processing corrosion resistance After cylindrical press processing, the processed part (side part) is JIS-
The white rust occurrence rate (%) after 2000 hours and the red rust occurrence rate (%) after 4000 hours were determined by a salt spray test based on Z-2321. (c) Paint adhesion The evaluation method was performed according to Figure 9. (d) Spot weldability The evaluation method was carried out in accordance with Fig. 13. (e) Sliding resistance The evaluation method was carried out according to Fig. 11. (f) Film adhesion The evaluation method was performed according to Figure 2. (g) Chemical conversion treatment property It was treated under standard conditions using a commercially available chemical conversion treatment bath (phosphate) and evaluated by observing the appearance. The evaluation method is as follows. ◎: Normal chemical conversion coating area 0% ○: Occurrence area 0-1% △:〃 1-10% ×:〃 10-50% However, it has been difficult to obtain an organic composite steel sheet that satisfies paint adhesion, weldability, and workability at the same time. In contrast, in the present invention, the proportion of Cr ₂ O ₃ in the chromate film on the plated steel sheet is 60% or more, and the total amount of chromium deposited is 40~40%.
An electrolytic chromate layer is formed with a copolymerization ratio of 120mg/ ^m2 , and an olefin copolymerization ratio of 70~70 is formed on top of it.
By applying an aqueous solution containing 15 to 40% colloidal silica of 1 to 10 mμ to an aqueous resin dispersion of 95% olefin/acrylic acid copolymer resin, and drying to form a film. , it is possible to produce an organic composite steel sheet that is extremely excellent in all of the above performances. Therefore, the organic composite steel sheet according to the present invention is particularly suitable for rust-preventing steel sheets for automobile bodies due to its excellent performance, and its economical effects are extremely large.

[Brief explanation of drawings]

Figure 1 shows the relationship between the ratio of Cr ₂ O ₃ in the electrolytic chromate layer of an organic composite steel sheet and the peelability of the film after press working, and Figure 2 shows the relationship between the ratio of Cr 2 O 3 in the electrolytic chromate layer of an organic composite steel sheet and the peelability of the film after press working. Figure 3, which shows the cylindrical drawing method, is a diagram showing the flat plate corrosion resistance of an organic composite steel sheet similar to Figure 1, and shows the relationship between the proportion of Cr ₂ O ₃ in the electrolytic chromate layer and corrosion resistance. It is something. Figure 4 is a diagram showing the relationship between the total amount of chromium deposited in the electrolytic chromate layer of an organic composite steel sheet and the peelability (blackening rate) of the film after press working. A diagram showing the relationship between corrosion resistance and flat plate corrosion resistance, Figure 6 is EG (electrogalvanized steel plate),
Figure 7 shows the elution of chromium when Zn-Fe alloy coated steel sheets and Zn-Ni alloy coated steel sheets are subjected to known chromate treatment. −Ni-based alloy plated steel plate and thin
A diagram showing the elution of chromium when an electrolytic chromate layer according to the present invention is formed on a Ni-plated steel sheet,
Figure 8 shows EG, Zn-Fe alloy coated steel sheets and Zn-
Figure 9 shows the corrosion resistance when a conventional chromate layer and an electrolytic chromate layer according to the present invention are formed on a Ni-based alloy plated steel sheet. Figure 10 is a diagram showing the effect on paint adhesion when changing the temperature. Figure 10 is a diagram showing the relationship between the copolymerization ratio of olefin and acrylic acid and corrosion resistance in olefin/acrylic acid copolymer resin.
The figure shows colloidal silica with different particle sizes added to an aqueous resin dispersion of olefin/acrylic acid copolymer resin with various copolymerization ratios of olefin and acrylic acid.
Figure 12 shows the relationship between the copolymerization ratio of olefin and acrylic, the particle size of colloidal silica, and sliding resistance. Figure 13 is a diagram showing the corrosion resistance of the processed part in the same case as Figure 13 is a diagram showing the relationship between colloidal silica particle size and weldability, Figure 14 is a diagram showing the relationship between colloidal silica particle size and weldability.
Figure 15 shows the relationship between the amount of colloidal silica added and sliding resistance, Figure 15 shows the relationship between the amount of colloidal silica added and corrosion resistance of processed parts, and Figure 16 shows the relationship between organic coating thickness and welding. Diagram showing the relationship with gender,
Fig. 17 is a diagram showing the relationship between the thickness of the organic film and corrosion resistance, Fig. 18 a, b, and c are cross-sectional views of the organic composite steel sheet of the present invention, and Fig. 19 is a diagram showing the relationship between the thickness of the organic film and the corrosion resistance. Or it is a figure which shows the relationship between the total chromium adhesion amount and chemical conversion treatment property in the case of forming an electrolytic chromate layer on a plating surface. DESCRIPTION OF SYMBOLS 1... Steel plate, 2... Plated layer, 3... Electrolytic chromate layer, 4... Colloidal silica-containing organic film,
5... Steel plate surface, 6... Plating surface, 7... Electrolytic chromate layer (total chromium amount ≦3 mg/m ² ).

Claims (1)

[Claims] 1. A plating layer is provided as a first layer on the surface of a steel plate, and a chromate layer has a ratio of Cr ₂ O ₃ as a second layer.
It has an electrolytic chromate layer with a total chromium content of 40 to 120 mg/m ² at 60% or more, and an electrolytic chromate layer with a total chromium content of 40 to 120 mg/m2.
An organic composite steel sheet having a 0.5-3μ thick water-based resin layer made of an olefin/acrylic acid copolymer with an olefin copolymerization ratio of 70-95% and containing 15-40% colloidal silica of 10 mμ. 2. The organic composite steel sheet according to claim 1, wherein the first plated layer is a Ni thinned layer. 3. The organic composite steel sheet according to claim 1, wherein the first plating layer is an alloy plating layer containing Ni. 4. The organic composite steel sheet according to claim 3, wherein the first plating layer is a Zn-Ni alloy plating layer. 5. The organic composite steel sheet according to claim 1, wherein the first plating layer is a multi-layer plating of Ni-free plating and thin Ni plating. 6. The organic composite steel sheet according to claim 1, having the first to third layers on both sides of the steel sheet. 7. The organic composite steel sheet according to claim 1, wherein the first to third layers are formed on one side of the steel sheet and the other side is a bare surface of the steel sheet. 8. The organic composite steel sheet according to claim 7, which has an electrolytic chromate layer on the surface of the steel sheet in which the proportion of Cr ₂ O ₃ in the electrolytic chromate layer is 60% or more and the total amount of chromium is 3 mg/m ² or less. 9. The organic composite steel sheet according to claim 7, which has a plating layer on the surface of the steel sheet. 10. The organic composite steel sheet according to claim 9, wherein the plating layer is a thin Ni plating layer. 11. The organic composite steel sheet according to claim 9, wherein the plating layer is an alloy plating layer containing Ni. 12. The organic composite steel sheet according to claim 9, wherein the plating layer is a Zn-Ni alloy plating layer. 13 Plating in which the plating layer does not contain Ni and Ni
Claim 9, which is multilayer plating with thinning
The organic composite steel sheet described in . 14 On the plating layer, the electrolytic chromate film
The ratio of Cr ₂ O ₃ is 60% or more and the total amount of chromium is 3
The organic composite steel sheet according to claim 9 or 10, which has a chromate layer of mg/m ² or less.